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  1. #1
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    On Demand Water Recirc

    I've got an idea and want to run it past you guys.

    I've got an ODW hot water heater at one end of our house (ranch). Naturally, it takes forever to get hot water to the other end of the house. Another note is that I'm on well water. Due to pressure/flow changes, the temp isn't consistent. This is not a big deal, but it is noticable.

    I've got a 40 gal electric tank that came with the house that I would like to incorporate. The heater has only 6 months on it.

    My idea was to do a recirc loop using the hot water tank as a buffer. If the ODW ever fails, I can use the electric tank. I was thinking of keeping it live but at a lower temp setting or have it on a disconnect.

    I need to have 3 gpm (per the manufacturer) and can size the pump needed myself. I plan on insulating all the lines as well.

    I know most manufacturers show a much smaller buffer tank. I don't know if what I want to do will have some unwanted side effects.

    Any input would be great!

    Stop, step back, relax and have another go at it.
    Last edited by BennyD; 03-27-2017 at 06:32 PM. Reason: Typo
    -----Stop, step back, relax and have another go at it.-----

  2. #2
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    Yeah, it will cost a fortune to run.

    Youd be better off getting a small point of use 5 gallon heater plumbed in series with the hot water supply line at the fixture you want hot sooner, by the time that tank would normally run cool, the on demand heater would take over.

    Or you could run an on demand recirc line alone, which is what I did in my house. The recirc is activated by a push button control and cuts out when the recirc line back at the heater is 90 degrees (adjustable)

    Beware, the on demand tankless needs a hefty pump to overcome the headloss of the coil.

    I found this out the hard way as I figured an NRF-33 would do the trick, as there was no head loss available for me to make a good pump selection. Ended up having to put 2 NRF-33 pumps in series to make the head I needed.


    Sent from my iPhone using Tapatalk

  3. #3
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    Having hot water right away is one of the nicest things you can do for yourself.
    I've solved this problem in two homes of mine. The first was a home I built. It was a two story with a basement. I ran the hot water pipe in a loop and returned it to the drain on the tank. All insulated. It was a thermal siphon. The hot water would naturally rise in the hot pipe, cool somewhat and return in the other pipe to the tank. I had a ball valve and check valve on the return line. The system worked great.

    In my 2nd house I finally installed a small electric heater in a closet. That water was the first at the faucet and the colder water from the other heater took over. Because this house is on a slab I couldn't do the thermal siphon thing. It also works great. Because the electric heater is small and well insulated it doesn't run much.
    Some here buy a little pump that takes hot water and pumps it back through the cold water line. That just makes the cold water not cold water. I don't really like that except if there are no other options.
    The thermal siphon was the best solution.
    Rereading your post I'm guessing a ODW is a demand heater yes? They are well known for temperature changes. Do you really need it?
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

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  5. #4
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    if the ODHW maker isnt designed for recirc you'll void the warranty and probably kill it. There are some, Navien and others, that are designed for recirc, and Navien has a specific setting for wells and fluctuating pressures.

  6. #5
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    Thread Starter
    I've got a Quietside that has a recirc diagram right in the IOM.

    Stop, step back, relax and have another go at it.
    -----Stop, step back, relax and have another go at it.-----

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  8. #6
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    then you should be fine. pipe it as the diagram and set the DIP switches, if any. your bills will increase but still be less than an standard tank, due to using the ODHW maker as a primary burner. basically, a glorified tank system.

    make sure you insulate all the hot lines and do not overpump the lines or erosion will result. 1/2 gpm is more than sufficient.


    PS - can you put a line of ~~~~~~ or ------- above your signature line? It screws me up all the time....

  9. #7
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    Thread Starter
    Quote Originally Posted by HVAC_Marc View Post
    then you should be fine. pipe it as the diagram and set the DIP switches, if any. your bills will increase but still be less than an standard tank, due to using the ODHW maker as a primary burner. basically, a glorified tank system.

    make sure you insulate all the hot lines and do not overpump the lines or erosion will result. 1/2 gpm is more than sufficient.


    PS - can you put a line of ~~~~~~ or ------- above your signature line? It screws me up all the time....
    Yeah, I'm not going for a "green" home here. I know my bills will go up some. Just a matter if it's worth it. To my wife, yes!

    I plan on insulating the lines and up the branches as well, at least to the sub floor. Going to wrap the tank too. I'll probably keep the hot water tank on a disconnect, only use it on a failure.

    Quietside calls for 3gpm on a recirc setup, I think I'll try to hit that #. At least a minimum of 2gpm.

    As for my signature, is this better? Lol

    Stop, step back, relax and have another go at it.
    -----Stop, step back, relax and have another go at it.-----

  10. #8
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    Quote Originally Posted by BennyD View Post
    As for my signature, is this better? Lol

    Stop, step back, relax and have another go at it.

    Better... now delete the first one

    you have 2 now. may be a function of your phone?

  11. #9
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    Thread Starter
    Just saw that... Wth

    Stop, step back, relax and have another go at it.
    -----Stop, step back, relax and have another go at it.-----

  12. #10
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    Thread Starter
    Quote Originally Posted by HVAC_Marc View Post
    Better... now delete the first one

    you have 2 now. may be a function of your phone?
    Ok, now?
    -----Stop, step back, relax and have another go at it.-----

  13. #11
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    Quote Originally Posted by BennyD View Post
    Ok, now?
    BETTER!!

    Thanks I was all messed up

  14. #12
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    Craptalk put it up in the body.
    -----Stop, step back, relax and have another go at it.-----

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  16. #13
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    I have no hard facts to back this up but in reading about energy savings it might be a waste of time $$ to insulate the HW tank. My understanding is modern insulation already in the tank should be enough. Can't hurt though.
    Your lucky that you can insulate pipes. I'm on a slab and while a slab offers some advantages, insulating pipes isn't one of them.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

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